Method for producing a hollow doublewall plastic article

ABSTRACT

A method for forming a hollow double-wall plastic article comprises positioning at least two tubular plasticized parisons of plastic material at opposite sides of at lease one core of a mold, closing half-molds of the mold about the parisons and the core to enclose said parisons, blowing the parisons into contact with the cavity faces by introducing fluid pressure medium into the parisons and removing the finished article from the mold after curing the article. Further, an apparatus for the said method comprises a pair of extrusion nozzles positioned parallel to each other, a mold including a pair of half-molds and means for introducing fluid pressure medium into the enclosed parisons.

Jan. 1972 TOMOMASU NAGAI 3'636151 METHOD FOR PRODUCE NE A HOLLOWDOUBLE-WALL PLASTIC ARTICLE Filed April 27. 1973 11 Sheets-Sheet 1 F G IF/G-Z 1 19 24 19 Jam. 18 1972 TOMOMASU NAGAI 3 3 151 METHOD FORPRODUCING A HOLLOW DOUBLE-WALL PLASTIC ARTICLE Filed April 27. 1970 11Sheets-Sheet 2 1972 TOMOMASU NAGAI 3,536,151

METHOD FOR PRODUCING A HOLLOW DOUBLE-WALL PLASTIC AR'i'ICLE Filed April27. 197-3 11 Sheets-Sheet 3 V ARU BU COOLING WATER CONTROL n- 1972TOMOMASU NAGAI METHOD FOR PRODUCING A HOLLOW DOUBLE-WALL PLASTIC ARTICLE11 Sheets-Sheet 4 Filed April 27. 197:)

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n- 1972 TOMOMASU NAGAI F/GJU Jan. 18, 1972 TOMOMASU NAGAI 3 53 151METHOD FOR PRODUCING A HOLLOW DOUBLEWALL PLASTIC ARTICLE Filed April 27,197C 11 Sheets-Sheet 6 Jan. 18, 1972 TOMOMASU NAGAI METHOD FOR PRODUCINGA HOLLOW DOUBLE-WALL PLASTIC ARTICLE 11 Sheets-Sheet 7 Filed April 27,1972 F/GJJ METHOD FOR PRODUCING A HOLLOW DOUBLE-WALL PLASTIC ARTICLE 11Sheets-Sheet 8 Filed April 27, 1970 FIG.

FIGJS METHOD FOR PRODUCING A HOLLOW DOUBLE-WALL PLASTIC ARTICLE 11Sheets-Sheet 9 Filed April 27. 1970 F/GJS an- 1972 TOMOMASU NAGAI METHODFOR PRODUCING A HOLLOW DOUBLE-WALL PLASTIC ARTICLE 11 Sheets-Sheet 10Filed April 27. 1973 Jan. 18, 1972 TOMOMASU NAGM 3,536,151

METHOD FOR PRODUCING A HOLLOW DOUBLE-WALL PLASTIC ARTICLE 11Sheets-Sheet 11 Filed April 27. 1979 United States Patent 3,636,151METHOD FOR PRODUCING A HOLLOW DOUBLE- WALL PLASTIC ARTICLE Tomomasu Nagai, Tokyo, Japan, assignor to Kyoraku Kogyo Co., Ltd., Kamigyo-ku,Kyoto, Japan Filed Apr. 27, 1970, Ser. No. 32,109 Int. Cl. B29c 17/07US. Cl. 26489 4 Claims ABSTRACT OF THE DISCLOSURE A method for forming ahollow double-wall plastic article comprises positioning at least twotubular plasticized parisons of plastic material at opposite sides of atleast one core of a mold, closing half-molds of the mold about theparisons and the core to enclose said parisons, blowing the parisonsinto contact with the cavity faces by introducing fluid pressure mediuminto the parisons and removing the finished article from the mold aftercuring the article. Further, an apparatus for the said method comprisesa pair of extrusion nozzles positioned parallel to each other, a moldincluding a pair of half-molds and at least one core member, means foropening and closing the half-molds and means for introducing fluidpressure medium into the enclosed parisons.

The present invention relates to a method and an apparatus for forming ahollow, double-wall plastic article such, for example, as the containersuitable for heat-insulation, the palette, the buoy, the caddy bag andthe like, and more particularly to a new and improved method and animproved apparatus for economically efiiciently producing such articlefrom a plurality of tubular pari sons of plastic material in oneblow-molding operation.

At the present time it has been known to form the hollow, double-wallconstruction such as bottles or the like by using blowmolding means inwhich the plastic material is extruded from a dual nozzle in the form ofa dual tubular parison which is of an inner parison section and an outerparison section coaxially surrounding the inner parison section andwhich has fluid pressure medium between the parison sections to preventundesirable welding of the both sections.

The said means is suitable for forming simple, small articles such ascylindrical bottles of circular shape in cross-section, but being notadequate to manufacture the somewhat complicated, double-wall articlessuch, for example, as rectangular or polygonal articles or the like.Further, construction of the die head having the said dual nozzle forextruding the dual parison is obliged to be much complicated. Moreover,the dual parison having entrapped fluid pressure medium between theparison sections is much too difficult to maintain itself in the proper,controlled working condition.

Accordingly, the one object of the present invention is to provide aunique improved method for forming the unitary structure of the largersized hollow article provided with double-wall from at least twoparisons of plastic material in one blow-molding operation. The subjectinvention is particularly applicable to the formation of structure ofthe described and other similar structures wherein cheapness as to cost,light weight, self-supporting rigidity and strength sufiicient tofulfill the purpose of the structures, ease of fabrication, and highstrength to weight ratio are advantageously combined.

In carrying out the invention in one aspect thereof, a method forforming a hollow double-wall plastic article is provided in which theprocess comprises the steps of positioning at least two tubularplasticized parisons of thermoplastic material on opposite sides of atleast one 3,636,151 Patented Jan. 18, 1972 ice core of the mold, closinghalf-molds of the mold about the parisons and the core to enclose saidparisons within a molding cavity defined by the half-molds and the core,and to pinch off excess parts of the parisons, blowing the parisons intocontact with the cavity faces by introducing fluid pressure medium intothe parisons thereby welding the expanded parisons to each other onadjacent portions with heat and internal pressure so as to form anintegral unitary article, and removing the article from the mold afterthe article is sufliciently cured by cooling the mold.

rSaid parisons are preferably extruded from appropriate nozzles ofextruder apparatus under semi-molten condition. If desired, air trappedbetween the parisons to be expanded and the cavity faces of the mold maybe withdrawn prior to expansion of the parisons.

Further the apparatus for performing this improved method has been builtand being in successful operation. A pair of extrusion nozzles in theapparatus are disposed parallel to each other through which semi-moltenplastic materials are downwardly extruded in the form of tubularparisons. Disposed under the extrusion nozzles is a mold comprising apair of half-molds and at least one core member, said half-molds beingmovably arranged around the core member so as to assume open and closepositions. In the open position of the half-molds, one of the extrudedparisons is disposed between the one halfmold and the core member, andother parison between the other half-mold and the core member. The saidmold is provided with a molding cavity defined by the inner surface ofthe half-molds and the outer surface of the core member in the closeposition for enclosing the parisons. To introduce fluid pressure mediuminto the enclosed parisons the conventional suitable means is provided.During the expanding stage of the parisons within the cavity of themold, said two parisons are sufficiently welded to each other atadjacent portions thereof whereby hollow, double-wall article can beobtained as an integral unitary structure.

Other objects and advantages of the subject invention will becomeapparent from reading the following detailed description and byreference to the accompanying drawings wherein:

FIG. 1 is a front view of the blow-molding apparatus according to thepresent invention;

FIG. 2 is a plan view, taken along the line 22 in FIG. 1, of theapparatus according to the present invention:

FIG. 3 is a vertical sectional view, on an enlarged scale, of the moldin the apparatus according to the present invention in which the mold isin the closed condition about the parisons;

FIG. 4 is a schematic layout of the apparatus according to the presentinvention;

FIG. 5 is a plan view of the container produced by the method andapparatus according to the present invention;

FIG. 6 is a vertical sectional view of the container taken along theline 6-6 in FIG. 5;

FIG. 7 is a vertical sectional view of the container taken along theline 7-7 in FIG. 5;

FIG. 8 is a similar view to the FIG. 6, but being sectioned taken alongthe line 8-8 in FIG. 5

FIG. 9 is a cross-sectional view of the container taken along the line99 in FIG. 6;

FIG. 10 is an enlarged perspective view, partially broken away, of thecontainer;

FIG. 11 is a cross sectional view, on an enlarged scale, of othermodified mold of the apparatus according to the invention, the moldbeing adapted to produce a palette;

FIG. 12 is a perspective view of the palette;

FIG. 13 is a cross-sectional view of the palette taken along the line 1313 in FIG. 12;

FIG. 14 is a vertical sectional view of the palette taken along the line1414 in FIG. 12;

FIG. 15 is a perspective view, partially broken away, of a caddy bagproduced by the method and apparatus with an appropriate mold;

FIG. 16 is a perspective View of half part of a housing of the caddybag;

FIG. 17 is a perspective view of a core member of the caddy bag, showingthe folded condition thereof;

FIG. 18 is a plan view of the core in the natural condition thereof;

FIG. 19 is an enlarged cross-sectional view of the caddy bag taken alongthe line 1919 in FIG. 15;

FIG. 20 is a perspective view of the other article embodied as anice-box in accordance with the present invention;

FIG. 21 is a vertical sectional view of the ice-box taken along the line2121 in FIG. 20; and

FIG. 22 is a vertical sectional view of the other embodiment of theice-box in which the foamy plastic material is injected between innerand outer walls thereof.

Referring now to the drawings 1 to 4 wherein like numerals have beenemployed to designate similar parts throughout the various figures, itwill be seen that one embodiment of the blow molding apparatus accordingto the present invention is illustrated by the numeral 10.

The apparatus includes a conventional extruder 11 having a pair of dieheads 12 spaced apart from each other. Each of the die heads 12 isprovided with a looplike opening or nozzle (not shown) through which thethermoplastic material, for example, as polyvinyl chloride,polyethylene, polypropylene, polystyrene, A.B.S. resin or the like iscontinuously downwardly extruded under semi-molten condition in the formof a tubular parison.

In order to maintain the material being extruded at the proper workingcondition, the die heads may be heated by any conventional means such aselectric heater (not shown) and the like. Preferably, the openings eachis provided with not circular but laterally elongated, oblong shape, sothat each of the tubular parisons extruded from the correspondingopenings may be a laterally elongated, oblong form in cross sectionthereof as shown in FIG. 2.

Under the die heads a mold is disposed. The mold comprises a pair ofcomplementary half-molds 14A and 14B, and a stational core 15 positionedtherebetween. The said half-molds are arranged for movement into and outof engagement about parisons extruded from the die heads. In this, wayit is desirable to move both half-molds simul taneously and atsynchronous speed. Therefore, in the embodiment shown in the FIGS. 1 and2, said half-molds 14A and 14B are supported by a moving frame 16 comprising a horizontal base portion 17, a pair of elevational portions 18Aand 18B upwardly extended from the ends of the base portion 17,respectively, and wheels 19 rotatably installed to the under surface ofthe base portion 17 at each corner thereof. One of the half-molds issecured to the one elevational portion 18A and other mold 143 to amoving platen 70 supported by a plunger 72 which co-operates with acylinder 71 actuated by suitable pressure fluid medium and secured tothe other elevational portion 18B. The said moving platen 70 has atlower end thereof a horizontal rack plate 20 having a first rack 21spaced apart from a second rack 22 which is partially formed on theupper surface of the base portion 17. Between the first and the secondracks a pinion wheel 23 is interposed in engagement with both racks,said pinion wheel 23 being supported rotatably by a stay 25 secured on acarrier 24. The said wheels 19 of the moving frame 16 are ridden onrails 26, formed on the upper surface of the carrier 24 and elongatedalong the same direction with that of the movement of the half-molds.

From the above mentioned arrangement, it will be understood that whenthe cylinder 71 is actuated by pressure .4 fluid medium, twocomplementary half-molds can be simultaneously at synchronous speedmoved to assume positions in which they are close to and at a distancefrom one another.

In accordance with the present invention, thus, one of the extrudedparison A is passed between left-hand halfmold 14A and the stationalcore 15 and the other parison B between right-hand half-mold 14B and thestational core 15. Each of the half-molds is recessed at 36 to definethe outer shell configuration of the article which is to be molded, andthe stational core 15 being adapted to define the inner shell portion ofthe article. Thus, half-molds 14A, 14B, when engaged, will define amolding chamber or cavity 27 between the inner surfaces of thehalf-molds and the outer surface of the stational core 15 as shown inFIG. 3. At upper portion the half-molds 14A and 14B are provided withopposite knife-edge formation 28, respectively, which are arranged topinch off the parisons A and B therebetween. Each of the half-molds alsohas at lower portion thereof a lower knife-edge formation 29 whichengages with a circular surface of the core 15 to pinch off the parisonstherebetween.

Upon closing half-molds 14A, 143 about the two extruded parisons withthe stational core, a portion of each of parisons is enclosed within thecavity 27. The halfmolds will pinch oif the upper end of the enclosedportion and simultaneously pinch off the lower end of the enclosedportion under assistance of the circular surface of the core 15 as shownin FIG. 3. The half-molds 14A and 14B carry means for introducingexpansion fluid into each enclosed portion or hollow parison section,said means comprising a pair of needles 31 which are mounted onhalf-molds 14A and 14B, respectively. Each needle 31 is projected intothe interior of the corresponding, hollow parison section through thewall thereof.

A source of compressed air is connected via conduits 32 to each needle,for introducing compressed air into each of the hollow parison sections,thereby expanding them into engagement with the cavity walls, whilecausing the parison sections to assume the shape of the cavity. Prior tothe expanding step, pre-blow of the parisons is conducted, if necessary.In the expanded condition each parison section forms half-portion of anarticle or container to be produced and being welded to one another atadjacent portions thereof against the other parison section by theeffect of the heat and the internal pressure. The half-molds 14A, 14Band the stational core 15 are cooled, as by cooling water ducts 33connected to a suitable source of cooling fluid. This cools and sets themolded plastic, causing it to retain the mold configuration, whereby anopen-topped double-wall container as shown in FIGS. 5 to 10 is easilyobtained.

In the illustrated container, the inner wall or shell 34 is approachedto the outer wall or shell 35 much closely. As the result, a problem ofundesirable welding together is duly arisen. There is a tendency thatthe parisons collapse at the upper portion of the half-molds as thelatter closes about the parisons and the stational core 15. If thisoccurs, at any point, the opposite wall portions of the parisons weldtogether, preventing subsequent expansion in the mold cavity. Therefore,the means are provided for controlling those portions of the parisonsintended to engage the faces of the cavity 27. The desirable control isprovided by evacuating or withdrawing air from between the cavity facesand the adjacent wall sections of the enclosed parisons. This may beaccomplished in various ways. In the illustrated embodiment, air iswithdrawn from bet-ween the cavity faces and the adjacent wall sectionsof the enclosed parisons via vacuum passages 37 which are provided withextremely small diameter, e.g. 0.5 mm. and which communicate withmanifold passages 38 through the halfmolds 14A, 14B and the stationalcore 15. Each of the manifold passages 38 communicates with anappropriate source of suction through a conduit 39.

When the half-molds 14A and 14B are closed about the parisons, air iswithdrawn from between the parisons and the cavity faces of the mold.All to be required is to relieve the pressure of air trapped between theparisons and the cavity faces, which traps while if otherwise airprevents the parisons from following the contour of the cavity 27 as thehalf-molds are closed about the parisons and the stational core 15. Thepassages 37 are so small as to pre vent the passage of plastic materialtherethrough, while being sufiicient to permit the desirable withdrawalof air. The withdrawal is conducted as the half-molds 14A and 14B closeabout the extruded parison, prior to the introduction of expansion fluidthrough the needles 31. The conduits 39 for the passages 37 also arecommunicated to the source of expansion fluid -via a suitable changeablevalue, so that the obtained product or container can be easily removedfrom the cavity faces by applying the pr%- sure of fluid between theouter wall of the container and the cavity faces.

The feeding of the raw plastic material, the opening and closing of thehalf-molds and the heating and cooling thereof, the Withdrawal of airfrom between the enclosed parisons and the cavity of the mold, theintroduction of expansion fluid and the feeding of the pressure of fluidbetween the product and the cavity face all are controlled by suitableprogramming means. The said controls are conventional, and therefore areonly schematically indicated in FIG. 4. It will be understood that theillustrated arrangement of the cooling water ducts 33 and the vacuumpassages 37 is schematic, and that the same are provided in sufficientnumbers at proper locations to achieve the desirable result.

Thus, with the method and apparatus illustrated in the FIGS. 1 to 4,there is provided, in one blow-molding operation, a hollow,double-walled plastic container formed with two parisons and havingwelding or mating part 42 as shown in FIGS. 5 to 10. The welding ormating part 42 serves as an essential part which is capable ofreinforcing the container and which separates inner and outer shells 34and 35 of the container to maintain spaces therebetween. The said FIG. 5shows a plan view of the container, and FIGS. 6 to 9 illustrate sectionstaken along the appropriate line in FIGS. 5 and 6, while FIG. 10 being aperspective view partially broken away.

It will be appreciated that the method and apparatus according to thepresent invention may provide with various molding articles by alteringthe configuration of the cavity 27, i.e. the recesses 36 of thehalf-molds 14A and 14B an outline of the core in accordance with thecontour of the desirable article to be produced.

FIG. 11 illustrates a modified mold according to the invention formanufacturing a hollow, double-walled plas tic palette as shown in FIGS.12, 13 and 14. This palette is provided with a pair of oblong,flat-sided holes 43 opened on the opposite side surface thereof, whichare adapted to insert forks (not shown) of the lift or the like. Theholes 43 are formed in parallel to each other and being extended fromone side surface 62 to the opposite side surface 63. Each of the holes43 has an intermediate portion between end openings thereof a reducedportion 43A which provides close engagement between the hole andinserted fork of the lift. In the FIG. 11 showing the mold for producingthe palette, like numerals are employed to designate similar parts tothe FIG. 3. The mold of the second embodiment, however, is provided witha pair of cores 15, instead of single stational core of the firstembodiment illustrated in FIG. 3, and each core being of two sectionsseparably assembled by suitable means (not shown). The recesses 36 ofthe half molds 14A and 14B and outer configuration of the cores 15define a chamber or cavity 27 corresponding to the contour of thepalette. In the illustrated palette, the inner and the outer Wallsthereof much closely, approaches to each other, and they being weldedtogether at spaced locations 61 for reinforcing the palette, althoughthis need not necessarily be done.

Where welding is desired, the half-molds 14A, 14B and the cores 15 areshaped accordingly.

According to the present invention a hollow, doublewalled caddy bagprovided with complicated construction as shown in FIGS. 15 to 19 alsocan be easily obtained. The caddy bag comprises two blow-moldingmembers, i.e. an outer member or housing 45 having an integral handle 55and an inserted core member 46, each member being capable of molding inone operation with the similar manner to the above-mentioned method. Inthis way, it is natural that the mold for each member should be shapedin accordance with the contour of the appropriate member. The outermember or housing 45 is provided with a number of vertically elongated,semi-circular recesses 47 in the inner surface thereof and beinggradually tapered down. Formed at the intermediate part of inner surfaceof the housing 45 is a circular flange 48 which is adapted for receiptof the lower edge of the core member 46. The core member also isprovided with a number of vertically elongated, semi-circular recesses50 on the outer surface thereof and has, in folded condition thereof, aplurality of axially elongated holes 49. The said recesses 50 oppose therecesses 47 of the housing, respectively, to provide a number of holes51 as the core member 46 is inserted in the housing 45 as shown in FIGS.15 and 19. The core member 46 is tapered corresponding to the interiorof the housing and comprising two sections 46A and 46B, one of which isformed of one parison and other of another parison. The both sections46A and 46B are welded to one another at a welding portion 56 which isformed at one edge along the longitudinal direction of the core member.Opposite edges 52 of the sections 46A and 46B are spaced apart from eachother as shown in FIG. 18, so that, when the core member 46 is insertedinto the interior of the housing 45 under the folded condition (FIG.17), projected portions 53 on the outer surface of the core member arebrought into close and strong contact with opposite projections 54 onthe inner surface of the housing 45 without use of any adhesive agentsor the like.

The holes 49 and 51 are adapted to carry golf clubs 57 (FIG. 16). Asshown in FIGS. 15 and 19, there is provided with an open-topped,elongated space 64 for the miscellaneous things, for example, such asgolf-balls, towels or the like. The said space 64 may be formed at anydesired position or be omitted by modifying the appropriate molds, ifdesired.

With above construction, the caddy bag is capable of being producedlightly and economically, while the contained golf-clubs being notbrought into contact with each other since the golf-clubs are supportedby the holes, respectively, thereby preventing the golf-clubs from beinghurt.

FIGS. 20 and 21 show another embodiment of the container in the form ofan ice box which is also produced by the above-mentioned method andapparatus with the appropriate mold, and FIG, 22 illustrating anotherembodiment of the ice box in which foamy internal composition 58 ofplastic material, for example, such as polyethylene, polypropylene,polystyrene, polyurethane or the like is injected between inner andouter walls through openings 59 by conventional manner, therebyproviding with more durability and resistance against dzformation andfurther enhancing adiabatic effect there- 0 The subject invention in itsbroader aspects is not limited only to the specific embodiments shownand described but departures may be made therefrom within the scope ofthe accompanying claims without departing from the principles of theinvention and without sacrificing its chief advantages.

What I claim is:

1. A method for forming a hollow, double-wall plastic article comprisingpositioning at least two tubular plasticized parisons of plasticmaterial at opposite sides of at least one core of a mold, closinghalf-molds of the mold about the parisons and the core to enclose saidparisons within a molding cavity defined by the halfmolds and the coreand further to pinch off excess parts of the parisons, blowing theparisons into contact with the cavity faces 'by introducing fluidpressure medium into the parisons thereby welding the expanded parisonsto each other at adjacent portions with heat and the internal pressureso as to form an integral single article, and removing the article fromthe mold after the article is sufficiently cured by cooling the mold.

2. A method as claimed in claim 1 wherein each of said parisons iscontinuously extruded from an appropriate nozzle of extruder apparatusunder semi-molten condition.

3. A method for forming a hollow, double-wall plastic article comprisingextruding two tubular parisons of semimolten, plastic material fromextruder apparatus to opposite sides of at least one core of a mold,closing halfmolds of the mold about the parisons and the core to enclosesaid parisons within a molding cavity defined by the half-molds and thecore and further to pinch olf excess parts of the parisons, withdrawingtrapped air from between the enclosed parisons and the cavity faces,expanding the enclosed parisons into contact with the cavity faces byintroducing fluid pressure medium into the parisons through needlesthereby welding the expanded parisons to each other at adjacent portionswith heat and the internal pressure so to form an integral singlearticle, cooling the mold until the article is suf ficiently cured, andremoving the article from the mold whereby a hollow, double-wall plasticarticle is capable of producing in one blow-molding operationeconomically and efficiently.

4. A method as claimed in claim 3- further characterized by providing astep of applying fluid pressure medium between the outer surface of thearticle and the cavity faces, prior to the removal of the article fromthe mold thereby facilitating the removal of the article.

References Cited UNITED STATES PATENTS 3,372,429 3/1968 Kato 1814 XFOREIGN PATENTS 384,780 4/1963 Japan 264-98 ROBERT F. WHITE, PrimaryExaminer A. M. SOKAL, Assistant Examiner U.S. Cl. X.R.

l85 BV; 264-90, 96, 98, 335

